JP2015178615A - biaxially oriented polypropylene film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polypropylene film that has an excellent tensile rigidity although it has a low flexural rigidity and is flexible, and therefore can be used suitably as a mold release film.SOLUTION: This invention provides a biaxially oriented polypropylene film in which the sum Eof a tensile elasticity Ein film longitudinal direction and a tensile elasticity Ein film width direction is 2.0 GPa or more and 5.0 GPa or less, and the sum Rof a loop stiffness Rin film longitudinal direction and a loop stiffness Rin film width direction is 20 mg or more and 300 mg or less.

Description

The present invention relates to a biaxially oriented polypropylene film that can be suitably used as a release film and has excellent tensile rigidity despite its low bending rigidity and flexibility.

  Biaxially oriented polypropylene film is excellent in transparency, mechanical properties, electrical properties, etc., so it is used in various applications such as packaging, mold release, tape, cable wrapping and electrical applications including capacitors. . In particular, since it has excellent surface releasability and mechanical properties, it is suitably used as a release film for various members such as plastic products, building materials and optical members.

  The required characteristics for the release film are appropriately set depending on the intended use, but generally the film is required to have low stiffness and high flexibility. Polyethylene films are widely used in release film applications by taking advantage of high flexibility. Bending rigidity and tensile elastic modulus are used as indicators of film stiffness. Polyethylene film has low bending elastic rigidity and high flexibility, but the tensile elastic modulus is also low, so the film is pulled by tension when bonded to the product. In some cases, it was difficult to reduce the film thickness. In addition, polyethylene films generally tend to suffer from defects such as fish eyes, and may be difficult to use in release film applications that require high quality such as for optical members.

  Polypropylene film, on the other hand, is less susceptible to fish eyes and has the characteristics of maintaining an appropriate tensile rigidity even when it is thinned. However, handling properties may be reduced due to high bending rigidity. . For example, Patent Document 1 describes the bending rigidity (loop stiffness value) of a polypropylene film, but the flexibility is insufficient. Moreover, since it was an unstretched film, the orientation of the film was weak and the tensile elasticity was insufficient. Patent Document 2 describes a biaxially stretched polypropylene film, which is excellent in tensile rigidity but has high bending rigidity and insufficient flexibility because a high crystal raw material is stretched at a high magnification. Met.

JP 2008-255233 A Japanese Patent Publication No. 09-001650

An object of the present invention is to solve the above-described problems. That is, an object of the present invention is to provide a biaxially oriented polypropylene film that can be suitably used as a release film and has excellent tensile rigidity despite its low bending rigidity and flexibility.

In order to solve the above-described problems and achieve the object, the biaxially oriented polypropylene film of the present invention has a value of the sum E _{MD + TD} of the tensile elastic modulus E _MD in the longitudinal direction of the film and the tensile elastic modulus E _TD in the width direction. It is 2.0 GPa or more and 5.0 GPa or less, and the sum R _{MD + TD} of the loop stiffness R _MD in the longitudinal direction of the film and the loop stiffness R _TD in the width direction is 20 mg or more and 300 mg or less.

  The biaxially oriented polypropylene film of the present invention can be suitably used as a release film because it is excellent in tensile rigidity despite its low bending rigidity and flexibility.

In the biaxially oriented polypropylene film of the present invention, the sum E _{MD + TD} of the tensile elastic modulus E _MD in the longitudinal direction and the tensile elastic modulus E _TD in the width direction is 2.0 GPa or more and 7.0 GPa or less. When the value of E _{MD + TD} is less than 2.0 GPa, when used as a release film, for example, when the film of the present invention is bonded to the surface of a product, the film is deformed by tension and wrinkles and the like enter. There is. Although the thickness of the release film may be increased in order to prevent wrinkles, the amount of resin may increase and productivity may decrease, or bending rigidity may increase and flexibility may decrease. When the value of E _{MD + TD} exceeds 7.0 GPa, the bending rigidity increases and the flexibility decreases, and the handling property as a release film may decrease. The value of E _{MD + TD} is more preferably 2.0 GPa or more and 5.0 GPa or less, and still more preferably 2.0 GPa or more and 4.0 GPa or less. In order to set the value of E _{MD + TD in} the above range, the raw material composition of the film is set in the range described later, the tensile rigidity is increased while reducing the bending rigidity, and the film forming conditions are set in the range described later, and the film is made high. It is preferable to obtain a biaxially oriented polypropylene film by stretching at a magnification.

Biaxially oriented polypropylene film of the present invention has a tensile modulus _{E TD} in the tensile elastic modulus _{E MD} and the width direction in the longitudinal direction of the film is preferably less respectively 0.8GPa least 3.5 GPa. Even if the value of E _{MD + TD} is 2.0 GPa or more and 7.0 GPa or less as described above, if either E _MD or E _TD is less than 0.8 GPa, the film tends to stretch when tension is applied to the film during use. Or the film may tear easily. If either the value of E _MD or E _TD exceeds 3.5 GPa, becomes the strength balance between the other direction is poor, or become the film tends tear, reduced flexibility increased flexural rigidity, releasing The handling property as a film for use may be reduced. The values of E _MD and E _TD are more preferably 1.0 GPa or more and 3.0 GPa or less, more preferably 1.1 GPa or more and 2.8 GPa or less, and most preferably 1.5 GPa or more and 2.7 GPa or less. In order to set the values of _EMD and _{ETD in} the above ranges, the raw material composition of the film is set in the range described later, the tensile rigidity is increased while the bending rigidity is reduced, and the film forming conditions are set in the range described later. The film is preferably stretched at a high magnification to obtain a biaxially oriented polypropylene film.

  In the present application, a direction parallel to the film forming direction is referred to as a film forming direction, a longitudinal direction, or an MD direction, and a direction perpendicular to the film forming direction in the film plane is referred to as a width direction or a TD direction.

In the biaxially oriented polypropylene film of the present invention, the sum R _{MD + TD} of the loop stiffness R _MD in the longitudinal direction of the film and the loop stiffness R _TD in the width direction is 20 mg or more and 300 mg or less. When the value of RMD _{+ TD} is less than 20 mg, the stiffness of the film is too low, and handling properties may be lowered when used as a release film. When the value of R _{MD + TD} exceeds 300 mg, the bending rigidity increases, the flexibility decreases, and the handleability as a release film may decrease. The value of R _{MD + TD} is more preferably 30 mg to 250 mg, and still more preferably 30 mg to 200 mg. In order to set the value of _{RMD + TD in} the above range, the raw material composition of the film is set in the range described later, the bending rigidity is reduced while increasing the tensile rigidity, and the film forming conditions and the thickness of the biaxially oriented polypropylene film are reduced. Is preferably within the range described below.

The biaxially oriented polypropylene film of the present invention preferably has a value of E _{MD + TD} / R _{MD + TD} of 0.010 or more. A large value of E _{MD + TD} / R _{MD + TD} is preferable because the film has excellent tensile rigidity despite having low flexural rigidity and flexibility, and has excellent handling properties as a release film. The value of E _{MD + TD} / R _{MD + TD} is more preferably 0.015 or more, still more preferably 0.020 or more, and most preferably 0.025 or more. The value of E _{MD + TD} / R _{MD + TD} is preferably as large as possible, but the upper limit is substantially about 0.100, more preferably 0.090 or less, and even more preferably 0.080 or less. In order to set the value of E _{MD + TD} / R _{MD + TD in} the above range, the raw material composition of the film is set in the range described later, the tensile rigidity is increased while reducing the bending rigidity, and the film forming conditions are set in the range described later. The film is preferably stretched at a high magnification to obtain a biaxially oriented polypropylene film, and the thickness of the biaxially oriented polypropylene film is preferably in the range described below.

  The biaxially oriented polypropylene film of the present invention preferably has a static friction coefficient μs in the longitudinal direction of the film of 0.5 or less. When μs exceeds 0.5, the slipperiness of the film is poor and wrinkles are formed during film formation, or when used as a release film, for example, when the film of the present invention is bonded to the surface of a product, May be easier to enter. μs is more preferably 0.45 or less, and still more preferably 0.4 or less. Although μs is preferably as small as possible, the lower limit is substantially about 0.1. In order to set μs in the above range, the raw material composition of the film is set in the range described later, easy slip particles are added to the surface layer, the crystallinity of the resin in the surface layer is increased, and the film forming conditions are described later. Preferably, the film surface is stretched at a high magnification to increase the orientation of the film surface.

  The biaxially oriented polypropylene film of the present invention preferably has a total haze of 2.0% or less. If the total haze exceeds 2.0%, the defect inspection may not be possible when the film is used for the purpose of performing the defect inspection after the release film is bonded, for example. The total haze is more preferably 1.0% or less, still more preferably 0.8% or less, and most preferably 0.5% or less. The total haze is preferably as low as possible from the viewpoint of transparency, but practically about 0.05% is the lower limit. In order to set the total haze to the above range, the raw material composition of the film should be in the range described below, and low stereoregular polypropylene should be used, and the cast conditions and longitudinal stretching conditions should be in the range described below. It is preferable to reduce the crystal.

  The biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage of 1.0% or less after treatment in the width direction at 110 ° C. for 1 hour. If the thermal shrinkage rate exceeds 1.0%, the film may be easily curled when there is a step in which the temperature is applied during use as a release film. The thermal contraction rate is more preferably 0.5% or less, still more preferably 0.3% or less, and most preferably 0.1% or less. Although a minimum is not specifically limited, A film may expand | swell too much, and about -1.0% is a minimum substantially. In order to make the heat shrinkage ratio in the above range, the raw material composition is in the range described later, and in particular, the content of the ethylene component having low heat resistance is reduced, longitudinal stretching conditions, transverse stretching conditions, heat setting conditions, It is preferable that the relaxation condition is within the range described later, and the heat yield is reduced while maintaining the strength and flexibility of the film.

  The biaxially oriented polypropylene film of the present invention preferably has a melting point Tm of 158 ° C. or higher. If the melting point is lower than 158 ° C., the heat resistance may be insufficient and the thermal shrinkage rate may be increased, or the content of the ethylene component may be large, so that the tensile rigidity may be reduced or fish eyes may be easily generated. Melting | fusing point Tm becomes like this. More preferably, it is 160 degreeC or more, More preferably, it is 163 degreeC or more. In order to make the melting point Tm within the above range, the raw material composition is within the range described later, and in particular, the content of the ethylene component having low heat resistance is lowered, the longitudinal stretching condition, the lateral stretching condition, the heat setting condition, the relaxation. It is preferable that the conditions are within a range described later.

  The thickness of the biaxially oriented polypropylene film of the present invention is appropriately adjusted depending on the application and is not particularly limited, but is preferably 0.5 μm or more and 100 μm or less. When the thickness is less than 0.5 μm, handling may be difficult, and when it exceeds 100 μm, the amount of resin increases and productivity may decrease, or bending rigidity may increase and flexibility may decrease. . Since the biaxially oriented polypropylene film of the present invention is excellent in tensile rigidity even when the thickness is reduced, the handling property can be maintained. In order to make use of such characteristics, the thickness is more preferably 1 μm or more and 20 μm or less, and further preferably 1 μm or more and 15 μm or less. The thickness can be adjusted by the screw rotation speed of the extruder, the width of the unstretched sheet, the film forming speed, the stretch ratio, and the like within a range not deteriorating other physical properties.

  Next, a preferable polypropylene raw material when used for a biaxially oriented polypropylene film will be described.

  In the biaxially oriented polypropylene film of the present invention, it is preferable to use at least two types of polypropylene raw materials (polypropylene raw material A and polypropylene raw material B). As the polypropylene raw material A, it is preferable to use a polypropylene raw material with high crystallinity in order to improve the tensile rigidity of the film. As the polypropylene raw material B, stereoregularity is provided in order to improve the flexibility of the film (decrease the bending rigidity). It is preferable to use a polypropylene raw material having a low viscosity.

  The polypropylene raw material A is preferably a polypropylene having a cold xylene soluble part (hereinafter referred to as CXS) of 4% by mass or less and a mesopentad fraction of 0.95 or more. If these are not satisfied, the film-forming stability may be inferior or the tensile rigidity of the film may be reduced.

  Here, the cold xylene-soluble part (CXS) refers to a polypropylene component dissolved in xylene when the film is completely dissolved in xylene and then deposited at room temperature, and has low stereoregularity. It is considered that it corresponds to a component that is difficult to crystallize due to low molecular weight. If many such components are contained in the resin, the tensile rigidity of the film may be inferior. Therefore, CXS is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. CXS is preferably as low as possible, but about 0.1% by mass is the lower limit. In order to obtain such polypropylene having CXS, methods such as a method for increasing the catalytic activity in obtaining a resin and a method for washing the obtained resin with a solvent or propylene monomer itself can be used.

  From the same viewpoint, the mesopentad fraction of the polypropylene raw material A is preferably 0.95 or more, more preferably 0.97 or more. The mesopentad fraction is an index indicating the stereoregularity of the crystal phase of polypropylene measured by a nuclear magnetic resonance method (NMR method). The higher the numerical value, the higher the crystallinity, the higher the melting point, and the higher the temperature. It is preferable because it is suitable for use. The upper limit of the mesopentad fraction is not particularly specified. In order to obtain a resin with high stereoregularity in this way, there are a method of washing resin powder obtained with a solvent such as n-heptane, a method of selecting a catalyst and / or promoter, and a composition as appropriate. Preferably employed.

  Further, as the polypropylene raw material A, the melt flow rate (MFR) is more preferably 1 to 10 g / 10 min (230 ° C., 21.18 N load), particularly preferably 2 to 5 g / 10 min (230 ° C., 21.18 N). The range of (load) is preferable from the viewpoint of film forming properties and tensile rigidity of the film. In order to set the MFR to the above value, a method of controlling the average molecular weight or the molecular weight distribution is employed.

  The polypropylene raw material A is mainly composed of a propylene homopolymer, but may contain other unsaturated hydrocarbon copolymerization components or the like within a range not impairing the object of the present invention. The coalescence may be blended. For example, ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, 3-methylbutene as monomer components constituting such a copolymer component or blend. 1,1-hexene, 4-methylpentene-1,5-ethylhexene-1,1-octene, 1-decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2- Examples include norbornene. From the viewpoint of tensile rigidity, the copolymerization amount or blend amount is preferably less than 1 mol% in terms of copolymerization amount and less than 10 mass% in terms of blend amount.

  Next, the polypropylene raw material B will be described.

  The polypropylene raw material B is preferably a polypropylene raw material having good compatibility with the above-mentioned polypropylene raw material A and low crystallinity and stereoregularity in order to improve flexibility and transparency. As such a polypropylene raw material B, amorphous polypropylene, low stereoregular polypropylene, syndiotactic polypropylene, α-olefin copolymer and the like can be used, but excellent transparency can be obtained with a small addition amount. Therefore, amorphous polypropylene and low stereoregular polypropylene are particularly preferable.

  As the polypropylene raw material B, the amorphous polypropylene preferably used is preferably mainly composed of a polypropylene polymer having mainly atactic stereoregularity, specifically, a homopolymer or a copolymer with an α-olefin. Can be mentioned. In particular, the latter, that is, an amorphous polypropylene-α-olefin copolymer is preferred. In the present application, the term “main component” means that the proportion of a specific component in all components is 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, most preferably Preferably it is 95 mass% or more.

  The amorphous polypropylene can be produced as a by-product of isotactic polypropylene during homopolypropylene polymerization. Since the glass transition temperature is lower than that of general polypropylene, it can be extracted as a boiling n-heptane (or xylene) soluble component of homopolypropylene. Alternatively, crystalline polypropylene can be polymerized independently by changing the catalyst and polymerization conditions. The amorphous polypropylene preferably used in the present invention can be used without particular limitation as long as it is produced by a conventionally known production method. Commercially available products such as “Tufselen” manufactured by Sumitomo Chemical Co., Ltd. can be appropriately selected and used as the amorphous polypropylene having the above characteristics.

  When an amorphous polypropylene-α-olefin copolymer is used as the amorphous polypropylene in the present invention, examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-octene and 1-decene. 4-methyl 1-pentene or propylene-ethylene-1-butene is desirable.

  Examples of amorphous polypropylene-α-olefin copolymers using such α-olefins include propylene / ethylene copolymers, propylene / ethylene / 1-butene copolymers, and propylene-1-butene copolymers. , Propylene / ethylene / cyclic olefin copolymer, propylene / ethylene / butadiene copolymer, and the like.

  The low stereoregular polypropylene preferably used as the polypropylene raw material B is preferably a homopolymer of propylene and produced using a metallocene catalyst as a polymerization catalyst. The melting point of the low stereoregular polypropylene is 100 ° C. or less, more preferably 60 to 90 ° C., and particularly preferably 65 to 85 ° C. The weight average molecular weight is preferably 40,000 to 200,000, and the molecular weight distribution Mw / Mn is preferably 1 to 3 (Mw: weight average molecular weight, Mn: number average molecular weight). As the low stereoregularity polypropylene having the above-described characteristics, a commercially available product such as “El Modu” manufactured by Idemitsu Kosan Co., Ltd. can be appropriately selected and used.

  The biaxially oriented polypropylene film of the present invention may contain branched polypropylene H in addition to the polypropylene raw material A and the polypropylene raw material B described above from the viewpoint of improving the tensile rigidity. When adding, 0.05-10 mass% is preferable, More preferably, it is 0.5-8 mass%, More preferably, it is preferable to contain 1-5 mass%. By containing the branched polypropylene H, the size of the spherulite produced in the cooling step of the melt-extruded resin sheet can be controlled to be small, and a polypropylene film excellent in transparency and strength can be obtained.

As the above-mentioned branched polypropylene H, the melt flow rate (MFR) is preferably in the range of 1 to 20 g / 10 minutes, and more preferably in the range of 1 to 10 g / 10 minutes, from the viewpoint of film formability. preferable. Moreover, about melt tension, what exists in the range of 1-30 cN is preferable, and what exists in the range of 2-20 cN is more preferable. Moreover, the branched polypropylene H here is a polypropylene having 5 or less internal 3-substituted olefins per 10,000 carbon atoms. The presence of this internal tri-substituted olefin can be confirmed by the proton ratio in the ¹ H-NMR spectrum.

  In the biaxially oriented polypropylene film of the present invention, the content of the ethylene component contained in the polymer constituting the film is preferably 10% by mass or less. More preferably, it is 5 mass% or less, More preferably, it is 3 mass% or less. The greater the ethylene component content, the lower the crystallinity and the easier it is to improve flexibility and transparency. However, when the ethylene component content exceeds 10% by mass, the tensile rigidity decreases or the heat resistance increases. It may be reduced or fish eyes are likely to occur.

  In the biaxially oriented polypropylene film of the present invention, the content of petroleum resin contained in the polymer constituting the film is preferably 5% by mass or less. More preferably, it is 3 mass% or less, More preferably, it is 1 mass% or less, and it is most preferable that petroleum resin is not included. Transparency and tensile rigidity can be achieved by adding petroleum resin. However, if the content of petroleum resin exceeds 5% by mass, the bending rigidity becomes strong and the flexibility is reduced. May be higher.

  In the biaxially oriented polypropylene film of the present invention, the content of the cycloolefin polymer contained in the polymer constituting the film is preferably 5% by mass or less. More preferably, it is 3 mass% or less, More preferably, it is 1 mass% or less, and it is most preferable that a cycloolefin polymer is not included. Heat resistance and tensile rigidity can be improved by adding a cycloolefin polymer. However, if the content of the cycloolefin polymer exceeds 5% by mass, the bending rigidity becomes strong and the flexibility decreases. In some cases, the transparency is lowered due to the compatibility problem, haze is deteriorated, and the raw material cost is increased.

  In the biaxially oriented polypropylene film of the present invention, the content of the polypropylene polymer contained in the polymer constituting the film is preferably 95% by mass or more from the viewpoints of compatibility between flexibility and tensile rigidity, transparency, and heat resistance. More preferably, it is 96 mass% or more, More preferably, it is 97 mass% or more, Most preferably, it is 98 mass% or more.

  In the polypropylene raw material of the present invention, various additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slip agent, an antistatic agent, an antiblocking agent, a filler, a viscosity are included within the range not impairing the object of the present invention. An adjusting agent, an anti-coloring agent, etc. can also be included.

  Among these, the selection of the kind of antioxidant and the amount added is important from the viewpoint of long-term stability. That is, the antioxidant is a phenolic compound having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more. Specific examples thereof include various ones. For example, 1,3,5-trimethyl-2,4,6-, together with 2,6-di-t-butyl-p-cresol (BHT: molecular weight 220.4). Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (for example, Irganox (registered trademark) 1330: molecular weight 775.2 manufactured by BASF) or tetrakis [methylene-3 (3,5-di-t- Butyl-4-hydroxyphenyl) propionate] methane (for example, Irganox (registered trademark) 1010: molecular weight 1177.7 manufactured by BASF) is preferably used in combination. The total content of these antioxidants is preferably in the range of 0.03 to 1.0 mass% with respect to the total amount of polypropylene. When there are too few antioxidants, a polymer may deteriorate in an extrusion process and a film may color, or it may be inferior to long-term heat resistance. When there are too many antioxidants, transparency may fall by the bleeding out of these antioxidants. The more preferable content is 0.1 to 0.9% by mass, and particularly preferably 0.2 to 0.8% by mass.

  A crystal nucleating agent can be added to the polypropylene raw material of the present invention as long as it does not contradict the purpose of the present invention. As described above, the branched polypropylene (H) has an α-crystal or β-crystal nucleating agent effect itself, but other α-crystal nucleating agents (dibenzylidene sorbitols, sodium benzoate, etc.) ), Β crystal nucleating agents (amide compounds such as potassium 1,2-hydroxystearate, magnesium benzoate, N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide, quinacridone compounds, etc.) and the like. . However, since excessive addition of the above-mentioned different kind of nucleating agent may cause a decrease in stretchability or a decrease in transparency and strength due to void formation, the addition amount is usually 0.5% by mass or less, preferably 0.1%. It is preferable to set it as mass% or less, More preferably, it is 0.05 mass% or less.

  The biaxially oriented polypropylene film of the present invention is obtained by biaxially stretching using the raw materials described above. The biaxial stretching method can be obtained by any of the inflation simultaneous biaxial stretching method, the stenter simultaneous biaxial stretching method, and the stenter sequential biaxial stretching method. Among them, the film forming stability, the thickness uniformity, In terms of controlling high rigidity and dimensional stability, it is preferable to employ a stenter sequential biaxial stretching method.

  Next, the structure of the film using the said polypropylene raw material is demonstrated.

  The biaxially oriented polypropylene film of the present invention preferably has a laminated structure of at least two layers from the viewpoints of both flexibility and high tensile rigidity, and transparency and slipperiness.

  In the biaxially oriented polypropylene film of the present invention, at least one layer (hereinafter referred to as “I layer”) in the laminated structure preferably contains 96% by mass or more of the polypropylene raw material A from the viewpoint of tensile rigidity. The content of the polypropylene raw material A in the I layer is more preferably 97% by mass or more, and still more preferably 98% by mass or more. When the content of the polypropylene raw material A in the I layer is less than 96% by mass, the orientation of the film is lowered and the tensile rigidity is lowered, and when there are many additive components having low heat resistance, the slipping property is lowered. There is a case.

  In the biaxially oriented polypropylene film of the present invention, at least one layer (hereinafter referred to as II layer) of the laminated structure has a mixing ratio of the polypropylene raw material A and the polypropylene raw material B of 10:90 from the viewpoint of flexibility. It is preferable that it is -95: 5 (mass ratio. The following is same). More preferably, it is 30: 70-90: 10, More preferably, it is 40: 60-85: 15. When the mixing ratio of the polypropylene raw material B in the II layer exceeds 90, stable extrusion becomes difficult and productivity may be lowered. If it is less than 5, the flexibility of the film may decrease.

  The biaxially oriented polypropylene film of the present invention has a laminate structure of at least two layers, and preferably includes at least one I layer and II layer described above. The thickness ratio of the I layer and the II layer in the thickness direction of the film is preferably 10% or more, more preferably 15% or more, and still more preferably 20% or more.

  In the biaxially oriented polypropylene film of the present invention, the surface layer is preferably an I layer from the viewpoint of slipperiness, and if the II layer is on the surface layer, the slipperiness may decrease due to blocking or the like. In addition, from the viewpoint of improving the slipperiness, easy slip particles may be added to the surface I layer.

  In the biaxially oriented polypropylene film of the present invention, it is preferable from the viewpoint of reducing the friction coefficient that at least one surface of the laminated structure contains easy-slip particles. The easy-slip particles are not particularly limited as long as the effects of the present invention are not impaired. For example, inorganic particles and organic particles can be used. Inorganic particles include silica, titanium oxide, aluminum oxide, zirconium oxide, calcium carbonate, carbon black, zeolite particles, and organic particles include acrylic resin particles, styrene resin particles, polyester resin particles, and polyurethane resin particles. Polycarbonate resin particles, polyamide resin particles, silicone resin particles, fluorine resin particles, or copolymer resin particles of two or more monomers used for synthesizing the resin. However, since the polypropylene resin has low surface energy, when the particles are added and stretched, the particle interface peels off during stretching, voids are generated, haze increases, and transparency may decrease. From the viewpoint of improving transparency, it is preferable to use the above inorganic particles or organic particles having a silane coupling treatment on the surface, and particularly preferred are silica particles having a silane coupling treatment.

  The average particle size of the easy-slip particles is preferably from 0.1 μm to less than 1.0 μm. If the average particle size is less than 0.1 μm, the particles may aggregate to form coarse particles, which may reduce transparency. When the average particle size is 1.0 μm or more, voids are likely to be generated at the particle interface during stretching, and transparency may be lowered. In addition, particles added to the surface layer may fall off during film formation, resulting in increased surface roughness or increased haze. The average particle size is more preferably 0.15 μm or more and less than 0.9 μm, and further preferably 0.15 μm or more and less than 0.8 μm. Moreover, you may use together two or more types of particle | grains from which an average particle diameter differs from a viewpoint of handling property improvement.

  The biaxially oriented polypropylene film of the present invention preferably has a laminate structure of at least two layers and includes easy-slip particles on at least one surface layer. At this time, the thickness of the layer containing easy-slip particles is preferably 0.2 to 2.0 μm. If it is less than 0.2 μm, the slippery particles may fall off during film formation. If it exceeds 2.0 μm, the haze may increase and the transparency may decrease. The thickness of the layer containing easy-slip particles is more preferably 0.2 to 1.6 μm, still more preferably 0.3 to 1.4 μm.

  The content of the easy-slip particles in the raw material of the layer containing the easy-slip particles is preferably 0.01% by mass or more and less than 1.0% by mass. If the content is less than 0.01% by mass, the effect of reducing the friction coefficient may not be obtained. If the content is 1.0% by mass or more, haze may increase and transparency may decrease. The content is more preferably 0.05% by mass or more and less than 0.9% by mass, and still more preferably 0.1% by mass or more and less than 0.8% by mass.

  Next, although the manufacturing method of the biaxially oriented polypropylene film of this invention is demonstrated, it is not necessarily limited to this.

  First, the polypropylene raw material A is supplied to a single screw extruder for the A layer, and the raw material obtained by dry blending the polypropylene raw material A and the polypropylene raw material B at a 50:50 (mass ratio) is supplied to the single screw extruder for the B layer. And melt extrusion at 200 to 260 ° C. After removing foreign substances and modified polymer with a filter installed in the middle of the polymer tube, the stacking thickness ratio is 1/8/1 with a multi-manifold type A layer / B layer / A layer composite T die. Then, it is discharged onto a cast drum to obtain a laminated unstretched sheet having a layer configuration of A layer / B layer / A layer. At this time, the cast drum preferably has a surface temperature of 10 to 40 ° C from the viewpoint of transparency, and preferably 40 to 90 ° C from the viewpoint of slipperiness. As an adhesion method to the casting drum, any method of an electrostatic application method, an adhesion method using the surface tension of water, an air knife method, a press roll method, an underwater casting method, etc. may be used. The air knife method is preferable because it is good and the surface roughness can be controlled. The air temperature of the air knife is 0 to 50 ° C., preferably 0 to 30 ° C., the blowing air speed is preferably 130 to 150 m / s, and a double tube structure is used to improve the uniformity in the width direction. Is preferred. Further, it is preferable to appropriately adjust the position of the air knife so that air flows downstream of the film formation so as not to cause vibration of the film.

  The obtained unstretched sheet is allowed to cool in air and then introduced into the longitudinal stretching step. In the longitudinal stretching step, an unstretched sheet is first brought into contact with a plurality of metal rolls maintained at 100 ° C. or more and less than 150 ° C., preheated to the stretching temperature, stretched 3 to 8 times in the longitudinal direction, and then cooled to room temperature. When the stretching temperature is 150 ° C. or higher, the orientation of the film becomes weak and the tensile rigidity may decrease. On the other hand, if the draw ratio is less than 3, the orientation of the film becomes weak and the tensile rigidity may be lowered.

  Next, the longitudinally uniaxially stretched film is guided to a tenter, the end of the film is held with a clip, and the transverse stretching is stretched 7 to 13 times in the width direction at a temperature of 120 to 165 ° C. If the stretching temperature is low, the film may be broken or the flexibility and transparency may be lowered. If the stretching temperature is too high, the orientation of the film is weak and the tensile rigidity may be lowered. Further, when the magnification is high, the film may be broken, and when the magnification is low, the orientation of the film is weak and the tensile rigidity may be lowered.

  In the subsequent heat treatment and relaxation treatment steps, the clip is heat-set at a temperature of 100 ° C. or more and less than 160 ° C. while being relaxed at a relaxation rate of 2 to 20% in the width direction while the clip is held in tension in the width direction, and subsequently 80 to The film is guided to the outside of the tenter through a cooling process at 100 ° C., the clip at the film end is released, the film edge is slit in the winder process, and the film product roll is wound up. Here, the relaxation rate is more preferably 5 to 18%, and still more preferably 8 to 15%, from the viewpoint of obtaining thermal dimensional stability. If it exceeds 20%, the film may be too slack inside the tenter, and the product may be wrinkled. If the relaxation rate is less than 2%, thermal dimensional stability may not be obtained. Further, the temperature at which relaxation is imparted is more preferably 100 ° C. or more and less than 140 ° C., and in order to improve the thermal dimensional stability at 110 ° C., more preferably 100 ° C. or more and less than 130 ° C. If the temperature at which relaxation is applied is 160 ° C. or higher, the film may be broken or the flatness may be deteriorated. If it is lower than 100 ° C., dimensional stability may not be obtained.

  The biaxially oriented polypropylene film of the present invention obtained as described above can be used in various applications such as packaging films, release films, sanitary products, agricultural products, building products, and medical products. Although it has a low bending rigidity and is flexible, it has excellent tensile rigidity, so that it can be preferably used as a release film.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) Film thickness Five points were measured using a micro thickness gauge (manufactured by Anritsu), and an average value was obtained.

(2) Tensile elastic modulus in the longitudinal direction and width direction (E _MD , E _TD )
A biaxially oriented polypropylene film was cut into a rectangular shape having a length of 150 mm in the test direction and a width of 10 mm as a sample. Using a tensile tester (Tensilon AMF / RTA-100 manufactured by Orientec), measurement was performed 5 times in an atmosphere of 25 ° C. and 65% RH according to the method defined in JIS-K7127 (1999), and the average value was calculated. Asked. However, the distance between the initial chucks was set to 50 mm, the tensile speed was set to 300 mm / min, and the point where the load passed 1 N after the start of the test was used as the origin of elongation.

(3) Loop stiffness
A biaxially oriented polypropylene film was cut into a rectangle having a length in the test direction of 300 mm and a width of 25.4 mm to obtain a sample. The bending stiffness (mg) was measured using a loop stiffness tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The loop length was 50 mm and the crushing distance was 5 mm. The measurement was performed using five samples having different sampling positions in the longitudinal direction and the width direction, and the average value was obtained.

(4) Total haze of film Using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.), the haze value at 23 ° C of the biaxially oriented polypropylene film of the present invention was determined according to JIS-K7136 (2000). (%) Was measured three times and the average value was used.

(5) Coefficient of static friction (μs)
Measurement was performed using a slip tester manufactured by Toyo Seiki Co., Ltd. As the measurement method, the non-contact surface with the cast drum of the biaxially oriented polypropylene film is attached to the bottom of the device in the measurement range with a double-sided tape, and the contact surface with the cast drum of the biaxially oriented polypropylene film is placed on the top of the device. Then, the sample was wound and set at the measurement start location, and the value when rubbed between the non-contact surface and the contact surface with the cast drum was measured, and the initial rise resistance value was calculated as the static friction coefficient (μs). The measurement was carried out three times in the longitudinal direction of film formation, and the average value was obtained.

(6) Thermal shrinkage after 1 hour treatment at 110 ° C. in the width direction About the width direction of the film, 5 samples of width 10 mm and length 200 mm (measurement direction) were cut out and marked as marked lines at positions 25 mm from both ends. And measure the distance between the marked lines with a universal projector to obtain the test length (l ₀ ). Next, the test piece is sandwiched between papers, taken out after heating for 1 hour in an oven kept at 85 ° C. with zero load, cooled at room temperature, and the dimension (l ₁ ) is measured with a universal projector. It calculated | required by the type | formula and made the average value of 5 the heat shrinkage rate.

Thermal contraction rate = {(l ₀ −l ₁ ) / l ₀ } × 100 (%)
(7) Melting point Tm of film
A biaxially oriented polypropylene film (5 mg) was sampled in an aluminum pan and measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). First, the temperature is raised from room temperature to 260 ° C. at a rate of 10 ° C./minute (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 20 ° C. at a rate of 10 ° C./minute. After maintaining for 5 minutes, the melting peak temperature observed when the temperature was raised again at 10 ° C./min (second run) was taken as the melting point of the film.

Example 1
Crystalline PP (a) (manufactured by Prime Polymer Co., Ltd., TF850H, intrinsic viscosity [η]: 1.8 dl / g, MFR: 2.9 g / 10 min, isotactic) as a polypropylene raw material for the surface layer (A) (Index: 96%) is supplied to a monoaxial melt extruder for the A layer, and as a polypropylene raw material for the core layer (B), 50 parts by mass of the crystalline PP (a) and a low stereoregular PP (b ) (Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g / 10 min, molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) 50 parts by mass were dry blended and uniaxial melt extrusion for the B layer And then extrude at 240 ° C, remove foreign matter with a 60μm cut sintered filter, and laminate with a feed block type A / B / A composite T die at a thickness ratio of 1/8/1. , CAS with surface temperature controlled to 30 ° C A cast sheet was obtained by discharging to the drum. Next, the film was preheated to 140 ° C. using a plurality of ceramic rolls and stretched 4.6 times in the longitudinal direction of the film. Next, the end portion was introduced into a tenter-type stretching machine by grasping with a clip, preheated at 160 ° C. for 3 seconds, and then stretched 8.0 times at 155 ° C. In the subsequent heat treatment process, heat treatment is performed at 120 ° C. while giving 10% relaxation in the width direction, and then the cooling process is performed at 100 ° C., leading to the outside of the tenter, the film end clip is released, and the film is wound around the core A biaxially oriented polypropylene film having a thickness of 12 μm was obtained. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 2)
98.65 parts by mass of crystalline PP (a), 1.25 parts by mass of silica particles SFP-20MHE (particle size: 0.3 μm, surface silane coupling treatment) manufactured by Denki Kagaku Kogyo Co., Ltd., and antioxidant IRGANOX 1010 manufactured by BASF Co., Ltd. is supplied to the twin screw extruder from the weighing hopper so that 0.1 part by mass is mixed at this ratio, melt kneaded at 240 ° C., discharged from the die in a strand shape, It was cooled and solidified in a water bath at 25 ° C. and cut into chips to obtain a polypropylene composition (c).

  98 parts by mass of the above crystalline PP (a) and 2 parts by mass of the above-mentioned polypropylene composition (c) are dry blended as a polypropylene raw material for the surface layer (A) and supplied to a uniaxial melt extruder for the A layer. As a polypropylene raw material for the core layer (B), the crystalline PP (a) 50 parts by mass and the low stereoregularity PP (b) (manufactured by Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g / 10 min. , Molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) 50 parts by mass are dry-blended and supplied to a uniaxial melt extruder for the B layer, melt-extruded at 240 ° C., and sintered at 60 μm cut After removing the foreign matter with a filter, it is laminated with a feed block type A / B / A composite T die at a thickness ratio of 1/8/1 and discharged onto a cast drum whose surface temperature is controlled at 50 ° C. Obtained. Next, the film was preheated to 140 ° C. using a plurality of ceramic rolls and stretched 4.6 times in the longitudinal direction of the film. Next, the end portion was introduced into a tenter-type stretching machine by grasping with a clip, preheated at 160 ° C. for 3 seconds, and then stretched 8.0 times at 155 ° C. In the subsequent heat treatment process, heat treatment is performed at 120 ° C. while giving 10% relaxation in the width direction, and then the cooling process is performed at 100 ° C., leading to the outside of the tenter, releasing the clip at the end of the film, and winding the film around the core A biaxially oriented polypropylene film having a thickness of 12 μm was obtained. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 3)
In Example 2, as a polypropylene raw material for the core layer (B), 70 parts by mass of the above crystalline PP (a) and low stereoregularity PP (b) (manufactured by Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g) / 10 minutes, molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) 30 parts by mass were used by dry blending, and a biaxially oriented polypropylene film was obtained in the same manner as in Example 2 except that. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

Example 4
In Example 2, as a polypropylene raw material for the core layer (B), 90 parts by mass of the crystalline PP (a) and low stereoregularity PP (b) (manufactured by Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g) / 10 min, molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) 10 parts by mass were used by dry blending, and a biaxially oriented polypropylene film was obtained in the same manner as in Example 2 except that. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Example 5)
In Example 2, 1.25 parts by mass of silica particle SILTON AMT-20S (particle size 1.7 μm, no surface treatment) manufactured by Mizusawa Chemical Co., Ltd. was used instead of silica particle SFP-20MHE manufactured by Denki Kagaku Kogyo Co., Ltd. Furthermore, in the heat treatment process after transverse stretching, heat treatment is performed at 150 ° C. while giving 10% relaxation in the width direction, and then the film is guided to the outside of the tenter through a cooling process at 150 ° C. to release the clip at the end of the film. The film was wound around a core, and a biaxially oriented polypropylene film was obtained in the same manner as in Example 2 except that. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 1)
In Example 2, the polypropylene composition (c) is used as the polypropylene raw material for the core layer (B) (the same raw material is used for the surface layer and the core layer), and other than that, biaxial orientation is performed in the same manner as in Example 2. A polypropylene film was obtained. The crystallinity of the raw material was high and the flexibility deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 2)
In Example 1, as a polypropylene raw material for the surface layer (A), 48 parts by mass of the crystalline PP (a) and low stereoregularity PP (b) (manufactured by Idemitsu Kosan Co., Ltd., El Modu S901, MFR: 50 g / 10 minutes, 50 parts by weight of molecular weight distribution Mw / Mn: 2, melting point: 80 ° C.) and 2 parts by weight of the above-mentioned polypropylene composition (c) are dry-blended and supplied to a uniaxial melt extruder for layer A, As the polypropylene raw material for the core layer (B), the same raw material as the polypropylene raw material for the surface layer (A) is supplied to the uniaxial melt extruder for the B layer. An oriented polypropylene film was obtained. The crystallinity of the raw material was low and the tensile rigidity deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

(Comparative Example 3)
In the transverse stretching step of Example 2, the transverse stretching magnification was 5.5 times, and a biaxially oriented polypropylene film was obtained in the same manner as in Example 2 except that. The thickness of the obtained film was 17 μm. Since the draw ratio was low, the orientation was weak and the tensile rigidity of the film deteriorated. Table 1 shows the physical properties and evaluation results of the biaxially oriented polypropylene film.

Claims (6)

The sum E _{MD + TD} of the tensile modulus E _MD in the longitudinal direction of the film and the tensile modulus E _TD in the width direction is 2.0 GPa or more and 7.0 GPa or less, and the loop stiffness R _MD in the longitudinal direction of the film and the width direction A biaxially oriented polypropylene film having a sum of _{RMD + TD} of loop stiffness R _TD of 20 mg or more and 300 mg or less. The biaxially oriented polypropylene film according to claim 1, wherein the value of E _{MD + TD} / R _{MD + TD} (GPa / mg) is 0.01 or more. The biaxially oriented polypropylene film according to claim 1 or 2, wherein a static friction coefficient µs in the longitudinal direction of the film is 0.5 or less. The biaxially oriented polypropylene film according to any one of claims 1 to 3, wherein the total haze is 2.0% or less. The biaxially oriented polypropylene film according to any one of claims 1 to 4, wherein a heat shrinkage rate after treatment at 110 ° C for 1 hour in the width direction of the film is 1.0% or less. The biaxially oriented polypropylene film according to any one of claims 1 to 5, which is used as a release film.